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Thread: Wiring Check / Resistor Help

  1. #1

    Default Wiring Check / Resistor Help

    Hello All,

    I had originally posted this in the 2010 Electronic Lightsaber w/ DVD Tutorial Thread, as it was a modification to an existing diagram there, but considering I was also looking for assistance with resistors I wasn't sure where to post this. (I'll remove whichever doesn't belong). But I was hoping someone might be able to chime in on this modified schematic for the 2010 Ani board.

    I was hoping to use a Tri Cree to mix purple, but I'm still a little soft on my knowledge of Ohms Law, and electronics as a whole. I read FJK's Ohms Law post (several times), and I've been reading everything I can possibly find on this great forum. I just need to validate that the schematic looks correct, and possibly get some help with which resistors I might need for my dies.

    Here is the schematic: Schematic Pic

    My math is as follows based on the specs from the Tri Cree product page in the store:

    Battery is 3.7v

    Red Cree
    80.6 Minimum Luminous Flux @ 350mA
    Forward Voltage @1000mA = 2.59v

    Royal Blue Cree
    600mW Minimum Radiant Flux @ 350mA
    Forward Voltage @1000mA = 3.41v

    RED: 3.7v - 2.59v = 1.11 ohms and 1.11ohms * 1amp^2 = 1.11watts for a 1.2ohm 1.25watt resistor - of which I was looking at the 1.2 ohm 3watt or a pot to dial-in the amount of red for the shade of purple I like... but I'm uncertain of what to go with.

    RBLUE: 3.7v - 3.46v = 0.29 ohms and 0.29ohms * 1amp^2 = 0.29watts for a 0.47ohm 0.5watt resistor ...also considering that the upper voltage for the RBlue is 4v or so, would I even need to resist this? I've read several posts with yes and no answers. I would edge for caution and chose to resist, but I just want to make sure that I have the knowledge one way or the other.

    AV: I had planed on using the 20mA DynaOhm Variable Resistor

    I appreciate any time you can spare.

    Thanks again!
    Last edited by Cralii; 12-10-2015 at 11:13 AM.

  2. #2


    The text for the resistor on your Red LED says ".47 ohm 3 watt" but links to the 1.2 ohm 3 watt resistor. The linked resistor is correct.

    It is always safer to use a resistor. I'd rather have a ~$0.50 part in my saber that is (probably) unneeded than to blow up a ~$15-$20 LED.
    We all have to start somewhere. The journey is all the more impressive by our humble beginnings. for the lazy man's resistor calculator! for getting resistor values the right way!

  3. #3


    Thank you, Silver, for the quick reply. Thank you for pointing out my typo/link error. I'm happy to ebb on the side of caution with the RBlue. Would definitely hate to fry my LED. Thanks for the input!

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